1. Field of the Invention
This invention relates to a double-walled tank for storing fluids such as heating oil, diesel fuel, and lubricating and hydraulic oils, with an inside container made of plastic, and an outside container made of sheet steel. In the invention, the outside container is provided with a container cover having openings for receiving sockets of the inside container. The inside container is a plastic container, preferably produced by blow molding. The outside container has a mechanical protective function and, furthermore, protects against leakage if the inside container should leak.
The outside container has, for example, a container jacket consisting of a U-shaped jacket sheet forming the container bottom and two side walls, as well as two end sheets joined with the jacket sheet. The end sheets and the jacket sheet are connected either by welding, or by a flange joint along the longitudinal edges. However, the outside container may also consist of a bottom sheet and a single or multi-part jacket shaped in the form of a "U", whereby the bottom sheet and the jacket can be tightly flanged or welded together (See German patent DE-OS 1 960 889).
2. The Prior Art
In practice, the cover of the outer container is screwed or riveted to the container jacket, or retained on the latter by means of spring clamps. The openings that pass through the sockets or threaded pipes of the inside container are provided with a blind ring for visual correction, and prevent rain water from penetrating the openings. However, there is no gas or liquid tight encapsulation of the jacket space between the inside and outside container. The tanks with the design known from prior art practical applications can be combined in assemblies of up to 25 units, and set up for storing heating oil without a brickwork tub for quantities of up to 25 cubic meters at the most. In furnace rooms, the stored quantity may not exceed 5 cubic meters. In water protected areas and in locations where old oils are stored, the tanks must always be set up in a brickwork tub that is sealed by a suitable protective paint coating. For leakage monitoring, provision is made for a leakage sensor located between the inside and the outside containers, which is installed in the container cover (See German patent DE 196 37 868 C1).